Building a roof rack deck on a GMT800 Suburban Z-71

[rayra]

Well today I wrestled around with removing the front factory cross bar and re-inserting the bolts in the front deck support bracket. Then I fabricated a new retention / safety strap to lay across the top side of the foremost support bracket, to mechanically 'lock-in' the deck boards.

I found everything still tight and in place, after ~200mi of freeway and around town driving. I haven't used any loctite as of yet, not sure I'm using the same fasteners, done working on things etc.
Haven't made a test drive yet, so no idea if this will eliminate the 65-70mph moan-drone. And the original topside fender washers were really stuck down into the plasticized paint. Wasn't fully cured when I rushed the assembly. So I didn't want to tear things up prying them loose. But that means the new top strap isn't laying flat on the deck, there's a very thin gap. So I might have just got rid of the moan and added a whistle. We shall see tomorrow.

 

[rayra]

Well I got some higher speed driving in today and I'm calling it tentatively 'solved'. Everything closed up, the 'moan' is greatly lessened, might be a tiny bit of a whistle now. But as soon as the sunroof is lifted up that all goes away and/or gets subsumed in the normal wind noise of the lifted sunroof.
I'm going to put some blue loctite on everything this weekend and call it done for now. My new double-din stereo / dash unit is inbound and also plan a minor suspension lift and shocks and a few other bits, shortly after. So this deck is probably staying this way the rest of the summer.

And I have to say it does indeed seem to be helping with cooling on the road. My AC is getting literally too cold. On a longer drive I wind up dialing it all the way back to '1' on the front AC only, rear off, with it 95F outside.

my next stages of temperature control will be attic radiant barrier material in the overhead above the headliner, and I'm researching UV-/infrared-blockign clear window film. But also window security film, maybe a combo product if I can find and afford it. I can do window tint myself, so I just have to find a material source.

 

[kojackJKU]

Thats pretty awesome. I am wanting to some sort of deck on my burb. I may rob your idea. I may use metal mesh type stuff to do it tho.

 

[rayra]

Thanks, feel free to. I went solid for the shade on the vehicle. I would have used plate aluminum if I could afford it.
Using expanded metal mesh would make a good solution for general cargo use.

I was also looking to keep as close to factory appearance as possible.

I've been thinking about inverting it, setting the cross braces to go up, such that the deck is flush with the top of the side rails. To create more of an air gap between deck and the roof skin. But I think I'd have to remake those braces with 3/4" square tubing for rigidity. I've made several long distance high speed drives since installing this and I've starting to get a little bend / lift in the rearmost flat-stock brackets. Right now I'm not sure if it's due to warping of the plywood or aerodynamic lift at the tail end, pulling it upward. Looking at it out the window right now it still seems to be as I built it. But I noticed the other day while washing the thing that the rear bracket was bent slightly away from the decking, as if the decking was pulled upward. now if it is flexing and changing position, that bracket will break and it will break at that bolt attachment location. So I'm considering at least replacing that rear bracket with tube stock for greater strength. And since the roof curves slightly front to rear as well as side to side, there's enough room at the rear brace for that 3/4 square tubing with things in the 'normal' arrangement.

I also need to do some experiments to isolate and eliminate the droning moan I've introduced with it. To start with, I'm going to tape up all the handhold cutouts. Then I might start cutting back the leading edge, movign it back out of the airflow. That SEEMS to be where the noise is originating, anyway.

 

[ROCKNROAD4X4]

Hey guys, just a quick thought, but a little late ...
I manufacture equipment for military, rescue, race and expedition vehicles.
Our main concept is using military spec(and higher) webbing straps and nets.
We could manufacture a custom made net to fit between roof rails to create a net base.
This is not trying to pee on your bonfire as your design looks superb, this is just another approach to the same problem.
We also make interior solutions to cargo storage.
All items are custom made per customer, so anything is possible.

 

[rayra]

interesting ideas and something I've discussed with our member Pappawheely for a top cover / shade / deck for his offroad box truck / photography business / camper build. I'd also initialyl discussed with him in his topic the idea of making a fabric deck a la those on catamarans. A nice sturdy design with perimeter reinforcement on the fabric panel and gusseting, laced onto the roof rack.

I'm still considering such a thing. And it too could be crafted in a split backboard-cum-fabric-stretcher design. Use a heavy zipper to connect the halves. Or even some other sort of fasteners on the rack rails, instead of lacing. But it's got to stay on at 80mph, too, not just sitting in camp.

Love to see some samples of your works.

 

[rayra]

edit, nevermind, wasn't really much of an update anyway. Suffice to say everything is still working / holding up, paint still looks good. Drone / moan is still there. About ready to experiment with that.

 

[flatboat]

droan or moan

Strictly for experiment . clear packaging tape on leading edge of cross bars to wood to stop wind from "singing " them just a thought

 

[rayra]

That's not a bad idea. But it's a deeper note, more of a moan than a whistle. The suburban roof is crowned both side to side and front to back. The noise appears to come from a couple feet back of the leading edge of the deck, which is just about the middle of the roof. I think the space between the flat deck and the arched roof is acting like a venturi or scramjet sort of thing. Air is entering the front and getting compressed, then expanding.
That or it's something akin to blowing across an open bottle, I've got (16) hand hold cutouts in the deck.

I also note that the moan effect seems to lessen when the moon roof is raised and air is diverted higher.

Next road trip I'm going to try it with the handhold holes taped shut, top and bottom. If that has no effect, I'm going to wedge-fit a tube of pipe insulation between the leading edge of the deck and the roof. try and block it off altogether. That certainly ought to have some effect. Worth trying anyway and fairly cheap to do and with no permanent mods.

But I'm still keen to sew a fabric cover and lace it on like a catamaran deck and give that a try instead of the wood deck.

 

[rayra]

Put the roof rack deck back on today, weather's starting to heat up. Still has wind noise / drone / moan. This time I left out the aerodynamic factory cross rails, which was another theory about venturi effects. Noise was apparent on the test drive so I went to Home Depot while I was out and got a piece of foam pipe insulation. The next corrective attempt is jamming the front gap between deck and vehicle roof, blocking airflow altogether.

If I still get a lot of noise I might go ahead and temp-tape the handhold holes. Just to test. If that eliminates the noise I'll have to figure a more permament / robust gap-filler. Maybe something like high-density foam inserts. Since the holes all have the flat metal strapping crossing them, I could try some heavy duty double sided tape on the metal straps, combined with cutting the foam plugs to be oversize, jamming them into the hole and onto the tape. Probably still won't be enough at 80mph.

Another solution might be to remake the deck and only partially jigsaw-cutting the handholds, like perforations. Cut 95% but not removed.

yet another solution may be to forego the cutouts altogether. Make the boards solid. And make some sort of webbing straps that can be added if the deck is ever pressed into service as a backboard / stretcher. Some little half-moon indents on the edges lined up over the cross braces, which a strap or rope carry handle setup would nestle into to keep things from sliding down the board.


I'm still intending to re-create the crossbraces with 3/4" or 1" square tubing, for rigidity. Probably be my first project when I get around to getting a wire-feed welding rig. Probably in the Fall. In the meantime I'm going to run it the way it is. Need the shade.

 

[ClovisMan]

So question...how much weight do you think the platform will hold. To give you an idea of what I mean well, I want something that I can do this on...

 

[rayra]

Make my four cross brackets out of 3/4" or 1" tubing, like the pictured platform, and you could walk around on it just fine. The plywood is plenty strong enough. The Z71 roof rack has very large footings front and rear and on the Sub, two smaller intermediate feet on the side rails and the side rails are slightly arched. I'm sure the whole thing can support quite a bit of weight without any issues.
Or make a complete frame much like a bedframe and suspend it within the Z71 side rails and that will certainly be strong enough.

 

[rayra]

another topic rescued from Photobucket's extortion.


I'm about to get a new sheet of ply and make the MkII Deck. Pretty sure now a large component of my noise is the handholds. But may still need the foam plugging the front.
Also, I started using an automatic car wash this Spring and the deck has taken some damage. Two of the handhold openings have had a paint failure and water intrusion, swelling the ply. So the MkII is going to have a couple applications of spar varnish on the edges, before painting. The Rustoleum Hammered Finish paint has otherwise help up great, even the top flat surfaces.

MkII is going to have panels of the same outline. Same mounting holes. I'll trim the panels about 1/8th" narrower in their width. The thick paint has made the fit very tight.
I'm also thinking to have a slight indent in their edges, aligned over the cross braces. If the panels are every pressed into service, the indents would serve as notches for a strap / rope wrapped around the panel to form handholds.

I'll be doing the MkII build in the next 2-3 weeks, so if you are interested check back into this topic then.

Still can't find a 4'x8' 3/16" or 1/4" thick sheet of aluminum for less than $400. Way more than I care to spend on this project.


10,670

 

[rayra]

well I pulled the MkI deck off this morning, making way for a fabric catamaran-style deck experiment and the solid MkII wood deck.

Here's a pic of the delamination. The water appears to have penetrated via the handhold cutouts in 3 of the 16, this pic is damage thru to the outer edge of the panel, from the handhold that is below it in this pic angle.

The problem didn't manifest until I recently started using an automated carwash. Don't know if it was the beating brushes or the high-pressure sprays. I'd been washing it myself with an RV brush every week or two, without apparent trouble.

For the MkII I'll be paying more attention to sealing the wood edges, probably with a spar varnish or possible some form of resin product. MkI I just did a heavy saturating layer of household latex primer. I also left the finished edges a little rough, hoping some 'tooth' would help the paint adhere better.
The Rustoleum Hammered finish paint helped up wonderfully, otherwise. The deck surfaces in the beating SoCal sun still look almost new, when clean. Still glossy, still cohesive. I intend to use that paint again on MkII. I'd say the failure was my priming / sealing process, not the topcoat paint.
I'll also look into using a proper primer in conjunction with the Hammered paint. I probably didn't. My application process was also very rushed with MkII. heavy primer application and not enough drying time. As soon as it was touch-dry I went right to the hammered paint application. Bad idea under any circumstances. It was hot as hell and I just wanted to get it done.

eta the foam pipe insulation also didn't hold up. First automatic car wash damaged / displaced it. Re-did it, high speed freeway trips (80mph) shoved it under. WOrking on a solution for that in MkII, too. I might extend the nose forward, closer to the sun roof. That would put it forward of the integral roof surface rails. That way the ends of the rails would be behind the foam and help wedge foam to stay in place. Previously the foam was compressed between the rails and deck, so there was nothing to prevent the foam sliding backward under windpressure. And the rail to deck spacing prevented there being much compression pressure on all the rest of the foamd span. ~44" wide, and only 6" of it the rails, so about 85% of the foam wasn't a tight fit. So no wonder the wind just shoved it back.

I really think a solid deck and a more secure front foam gasketing should resolve any of the added wind noise. Just in time for me to put a light bar and solar panel up there and start a new round of noise issues. heh.

 

[Stryder106]

I can stand on mine just fine - but it isn't wood. Mine is 1" tubing and heavy mesh. Due to wind noise mine is getting a front plate added from the bottom bar to my roof.